Currently, with the acceleration of the replacement of copper cables with optical fiber cables, construction of passive optical networks develops quickly, and therefore installation, acceptance testing, and routine maintenance need to be performed for the PONs. In addition, an optical time domain reflectometer (Optical Time Domain Reflectometer, OTDR) plays an important role in fiber network testing, fault locating, rectifying, and the like.
The OTDR needs to be capable of detecting extremely weak and extremely strong test signals. Therefore, it is required that a transimpedance amplifier (Transimpedance Amplifier, TIA) in the OTDR system have a high sensitivity and a large receiver dynamic range. In one aspect, improvement of the TIA sensitivity easily results in receiver saturation when a TIA input signal is relatively strong, and in another aspect, due to a limitation of an existing power supply capability, the receiver dynamic range of the TIA cannot be further enlarged. Therefore, a detection range of an OTDR test signal is relatively small in the prior art.